Preparation of polyvinylchloride

ABSTRACT

Process for preparing an improved polyvinyl chloride comprising polymerizing vinyl chloride in the presence of a peroxide and/or azo compound as catalyst, a protective colloid and in the additional presence of 1 to 20 weight percent referred to the vinylchloride of a polyvinylchloride including an emulsifier, the polyvinyl chloride having a particle size of 0.03 to 2.0 Mu , introducing a salt of a bivalent or trivalent metal to precipitate the emulsifier which has been introduced with the polyvinylchloride emulsion, and recovering the polyvinylchloride product of improved properties thereby formed.

United States Patent Meyer [54] PREPARATION OF POLYVINYLCHLORIDE [72]Inventor: Giinther Meyer, Sieglas Augustinusstn, Germany [73] Assignee:Dynamit Nobel Aktiengesellschaft,

Troisdorf, Germany [22] Filed: March 27, 1969 [21] Appl. No.: 811,208

[30] Foreign Application Priority Data March 30, 1968 Germany ..P 17 70094.6

[52] US. Cl. ..260/85.5 XA, 260/863, 260/87.1, 260/87.5 R, 260/875 G,260/87.7, 260/928 [51] Int. Cl. ..C08f I/ll, C08f 3/30, C08f 15/02 [58]Field of Search...260/92.8, 87.5, 85.5 XA, 86.3, 260/871, 87.7

[56] References Cited UNITED STATES PATENTS 3,370,105 2/1968 DeBell etal ..260/880 51 Oct. 10, 1972 3,436,440 4/1969 Abe et al. ..260/880FOREIGN PATENTS OR APPLICATIONS 1,087,390 10/1967 Great Britain..260/92.8 W

Primary Examiner-Joseph L. Schofer Assistant Examiner-John A. Donohue,Jr. Attorney-Burgess, Dinklage & Sprung [57] ABSTRACT 9 Claims, NoDrawings PREPARATION OF POLYVINYLCHLORIDE This invention relates to aprocess for preparing improved polyvinylchloride.

More particularly this invention relates to a process for preparingpolyvinylchloride characterized by properties which allow forsatisfactory working and suitability for most applications.

It is in the prior art to polymerize vinyl chloride using the suspensionmethod. Organic catalysts are used in these processes, for example,peroxides or azo compounds and protective colloids, such as gelatins,methyl cellulose or even polyvinyl alcohols, are also used in thisconnection.

The suspension polymers prepared on the basis of the prior artprocedures, however, are not of such a quality as to satisfy mostproduction and application engineers. A more or less wide particle sizedistribution is obtained, i.e., 30 to 300 microns having a nonuniformparticle structure ranging from transparent, dense particles to porousgranules of varying diameter. Numerous efforts have been made to arriveat a more regular and more readily processable particle material byvarying the polymerization conditions. The proposals so far have failedto solve the so-called Stippen" problem (speck formation), i.e., theunexpected occurrence of inhomogeneities in the final products.

In order that the problem of speck formation be kept at a minimum, themanufacturer requires polymer materials, i.e., particles, that can beworked up uniformly, but this requirement has not as yet been completelycomplied with.

The actual cause for the formation of specks has not previously beendetermined. However, the following may be considered as constitutingrequirements which must be satisfied if speck formation is to be.eliminated:

a. the formation of uniform PVC particles having a narrow range ofparticle size, and

b. the prevention of cross-linking reactions with the protectivecolloid.

In the processes of the prior art, a ratio of water to vinylchloride ofsubstantially 2 to I has been used.

The quantity of protective colloid amounts to between i and 0.5 percentand that of the catalyst to from 0.05 to 1 percent based on the quantityof the monomer. On the basis of these formulations, the particlestructures and particle-size distributions described above are obtained,but they are not uniform. A particular particle form is obtainedaccording to British Patent 796,309, which additionally uses emulsifiersof the alkyl sulfonate or aryl alkyl sulfonate type in the fonn of theircalcium and magnesium salts, respectively. A similar procedure isfollowed in the process described in German Green Patent 1,236,783,which uses polyamines in place of the alkyl sulfonates. A disadvantageof these procedures is that water-soluble emulsifier additives suppressthe action of the protective colloid system in suspension polymerizationand produce more or less shapeless or broken particles hav ing a porousstructure. These disadvantages are obviated according to the above-citedBritish patent by forming difficulty soluble alkaline-earth salts fromthe water-soluble emulsifiers. The interaction of these salts with theprotective colloid results in a PVC having an especially loose andporous structure. The plasticizer absorption, as determined by theoil-spot method amounts to about 38 percent for a product of this typeThe particle size distribution of such products, however, is stillunsatisfactory, and varies greatly according to the type of autoclaveused and the nature of the stirring during the polymerization. Inaddition to the polymer recovered in usable particle sizes, very fineparticles are also present which particles have an adverse effect onthefree-flowing quality of the PVC powder. if a more uniform processabilityis to be achieved, it is necessary in this case to classify, i.e., gradeor screen the polymer powder. Furthermore, the bulk weight, which isimportant with regard to the subsequent plastification in extruders, istoo low, i.e., the bulk weight amounts to less than 0.4.

Attempts have also been made to improve the plasticizability ofpolyvinylchloride polymers in the processing procedures by, for example,modifying the stirring conditions in the polymerization and increasingthe protective colloid content. There has thereby been obtained a veryfine but dense particle material. The

plasticizer absorption of this type of particles is, however, poor,amounting to less than I 5 percent.

All of the aforesaid and remaining known methods produce PVC powderswhich contain specks, the same having been caused by the wide range ofgrain sizes and/or by cross-linking in the particles.

in accordance with the invention it has now been found that suspensionpolymers having a narrow range of particle sizes, good dry-blendstructure and uniform particle shapes can be made by carrying out thepolymerization in the presence of l to 20 percent and and preferably 3to 8 percent referred to the weight of the monomer, of apolyvinylchloride emulsion containing an emulsifier, preferably in theform of a latex having a particle size of 0.03 to 2.0 microns,preferably 0.3 to 0.5 microns, and thereafter precipitating the emulsifier introduced in the emulsion polyvinyl chloride emulsion by theaddition of salts of bivalent or trivalent metals thereto.

The process is carried out iii the following manner:

A fully polymerized emulsion PVC latex is introduced into an agitatorautoclave in addition to water, a protective colloid and a catalyst. Theemulsifier that is introduced with the latex is made insoluble by theintroduction of bivalent or polyvalent metal cations, i.e., bivalentand/or polyvalent metal salts. Following the evacuation of the reactionvessel, gaseous vinyl chloride monomer is injected into the vessel andpolymerized therein at the desired temperature.

The speed of the stirring and the shape of the autoclave can be variedgreatly without afi'ecting the dryblend structure, particle structureand narrow particle size distribution of the polymer product.

Surprisingly, a polymer of unifonn particle shape is obtained, in whichthe particle sizes fall within a very narrow range, and having adry-blend structure which is good, i.e., the particles have a uniformand high porosity. Any particle size selected, from about 50 to 200microns, can be obtained as desired, although it can be made larger orsmaller by varying, for example, the protective colloid content of theemulsion or the stirring speed. About percent of the particles of theproduct will fall within a range of sizes which varies only by about 20to no more than 50 microns. Microscopic examination of the polymerparticles shows that the particles have a substantially uniform size andparts of lauroylperoxide, and

0.375 parts of CaCl were introduced into a one cubic meter autoclaveprovided with stirrer. A vacuum was then established in the autoclaveand 250 parts of vinyl chloride were introduced therein. Thepolymerization was carried out at 66C and 150 rpm. After 7 hours thereaction had ended.

The PVC which was recovered had a sieve analysis of 90 percent between land 120 microns, a bulk density of 0.435 and a plasticizer absorption of35 percent.

EXAMPLE 4 Example 3 was repeated with the same materials and usingsimilar quantities, but using an emulsion PVC latex having a K value of70in place of the PVC latex of Example 3. The polymerization was carriedat 53C and continued until a pressure drop occurred.

The product had a K value of 70. The product which was obtained had thesame sieve analysis as that set out in Example 3 and had a pore volumeof 50 percent by volume. The plasticizer absorption amounted to 43percent.

When in place of the methyl cellulose, the same amount of polyvinylalcohol was used (prepared from polyvinyl acetate having a molecularweight of 50-80 by saponification, degree of saponification 80-90percent), similar results were obtained.

EXAMPLE 5 Example 3 was repeated, but in this instance an emulsion PVClatex whose K value amounted to 60 and whose average particle sizeamounted to (a) 0.25 and (b) 0.5 micron was employed. The polymerizationtemperature was 65C and in place of the calcium chloride, 0.5 parts ofmagnesium chloride 6 H 0 was used. The polymer which was recovered hasthe same properties as set out in Example 3. The same results wereobtained when azo-bis-isobutyronitrile was used as the catalyst insteadof lauroyl peroxide, in quantities of 0.1 to 0.3 percent referred to themonomeric vinyl chloride.

lclaim:

1. Process for the preparation of polyvinylchloride comprisingpolymerizing vinylchloride in suspension in an aqueous medium bycontacting such under suspension polymerization conditions with apolymerization catalyst selected from the group consisting of peroxideand azo compounds, a protective colloid and an emulsion ofpolyvinylchloride containing emulsifier, which polyvinylchloride ispresent in a proportion of l to 20 weight percent referred to thevinylchloride monomer, and has a particle size of 0.03 to 2.0 p;introducing a salt of a polyvalent metal thereinto; precipitating theemulsifier introduced with said polyvinylchloride emulsion by said salt;and thereafter recovering the vinylchloride polymer thus formed.

2. Process according to claim 1 wherein said polyvinylchloride ispresent in an amount of 3 to 8 weight percent referred to thevinylchloride monomer and said polymerization is carried out at 30 to C.

3. Process according to claim 1 wherein said polyvinylchloride has aparticle size of 0.3 to 0.5 p.

4. Process according to claim 1 wherein said polyvinylchloride is in theform of a latex.

5. Process according to claim 4 wherein said latex has a solids contentof between 20 and 60 percent by weight.

6. Process according to claim 1 wherein said catalyst is a memberselected from the group consisting of lauroyl peroxide, caproylperoxide, benzoyl peroxide, keto peroxide, persulfates, andazoisobutyric acid.

7. Process according to claim 1 wherein said protective colloid is amember selected from the group consisting of methyl cellulose, gelatinwater-soluble starches, polyvinyl alcohols, polyacrylic acid, talc andkaolin.

8. Process according to claim 1 wherein said salt is a member selectedfrom the group consisting of chlorides, sulfates, nitrates and acetatesof calcium, magnesium, aluminum, strontium, barium, tin and zinc.

9. Process according to claim 1 wherein there is additionally present amonomer selected from the group consisting of vinyl acetate, vinylidenechloride, vinyl ether, acrylonitrile, acrylic acid ester and methacrylicacid ester in an amount of up to 10 percent by weight of total monomerpresent.

III i III i mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPatent No. 3 97,493 Dated October 10, 1972 Inventofls) GUNTHER MEYER Itis certified that: error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Title Page, line .6 of Abstract, before "including I insert -emulsion-Column 2, line 7, "onthe" should be -on the-- Signed and sealed this20th day of November 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. RENE D. TEGTMEYER Attesting Officer ActingCommissioner of Patents

2. Process according to claim 1 wherein said polyvinylchloride ispresent in an amount of 3 to 8 weight percent referred to thevinylchloride monomer and said polymerization is carried out at 30* to80*C.
 3. Process according to claim 1 wherein said polyvinylchloride hasa particle size of 0.3 to 0.5 Mu .
 4. Process according to claim 1wherein said polyvinylchloride is in the form of a latex.
 5. Processaccording to claim 4 wherein said latex has a solids content of between20 and 60 percent by weight.
 6. Process according to claim 1 whereinsaid catalyst is a member selected from the group consisting of lauroylperoxide, caproyl peroxide, benzoyl peroxide, keto peroxide,persulfates, and azoisobutyric acid.
 7. Process according to claim 1wherein said protective colloid is a member selected from the groupconsisting of methyl cellulose, gelatin water-soluble starches,polyvinyl alcohols, polyacrylic acid, talc and kaolin.
 8. Processaccording to claim 1 wherein said salt is a member selected from thegroup consisting of chlorides, sulfates, nitrates and acetates ofcalcium, magnesium, aluminum, strontium, barium, tin and zinc. 9.Process according to claim 1 wherein there is additionally present amonomer selected from the group consisting of vinyl acetate, vinylidenechloride, vinyl ether, acrylonitrile, acrylic acid ester and methacrylicacid ester in an amount of up to 10 percent by weight of total monomerpresent.